The present invention relates to a mandrel for providing internal support during the cold bending of large diameter pipes. In particular, the present invention relates to a mandrel having spring members that are adapted to bias against an internal surface of a pipe during cold bending to prevent buckling and distortion.
Mandrels are well known for providing internal support to a pipe to avoid buckling or wrinkling of the pipe wall while the pipe is being bent. For example, as disclosed in U.S. Pat. No. 3,834,210 to Clavin, et al., a mandrel apparatus is known for use with a pipe bending apparatus for bending large diameter pipes of the type used for oil and gas pipelines. The pipes used in such pipelines are typically formed of steel and can have a wall thickness in excess of one inch and a diameter in excess of forty-eight inches. Hence, a mandrel apparatus must be very robust to withstand the tremendous forces necessarily used when bending large pipes of this type.
A typical mandrel (e.g., as disclosed in U.S. Pat. No. 4,352,285 to LaRue, et al.) used in bending large diameter pipes includes semi-cylindrical support assemblies which are radially movable toward and away from one another in the plane of bending. For example, if the pipe will be bent in the vertical plane, then the mandrel will have top and bottom support assemblies which are vertically movable with respect to one another. After the mandrel is positioned within the bore of the pipe at the position designated for the bend, the support assemblies are moved radially outward into contact with the interior walls of the pipe and biased to exert an outward force. External forces are then applied to the pipe, bending it to form the desired configuration. During the bending process, the support assemblies of the mandrel deflect to remain in contact with the interior of the pipe walls. The outward force provided by the support assemblies prevents the walls of the pipe from bending inward to form buckles or wrinkles.
Mandrels of the type disclosed in U.S. Pat. No. 4,352,285 have support assemblies which include a plurality of buckle-resistant spring units. Each spring unit is formed of several elongate flat springs fastened together in a laminar stack. The spring units are fastened longitudinally to a plurality of transversely oriented arcuate support segments to form a semi-cylindrical array. The arcuate support segments are, in turn, mounted to spring plates that can be moved with respect to one another to move the support assemblies into the desired position.
During bending, the pipe wall farther from the center of bending is subjected to tension forces and the pipe wall nearer to the center of bending is subjected to compression forces. The support assemblies, which maintain contact with the pipe walls during bending, are likewise subjected to substantial tension and compression forces. These forces, along with the deflection of the spring units, urge elements of the spring units to shift with respect to one another.
The compression forces imposed on the mandrel during the bending of a pipe are large. Because of such forces, components of the mandrel are likely to break and/or become nonfunctional. The bolts attaching the bottom (tension-side) spring units to the support segments frequently break. As the region of the pipe being bent compresses on the mandrel, a shearing force is created between the spring units and the support segments. If the shearing force is greater than the shear strength of the bolt, the bolt breaks leaving a portion of it buried within the support segment. Then, the remains of the bolt must be removed and replaced to prevent an improper bend and/or buckling in the pipe. Much time and effort is required to remove and replace a broken bolt imbedded in a support segment, thereby delaying the production of a bent pipe.
Therefore, a need exists for a mandrel that is not only durable and effective for bending pipe, but which can also be easily repaired and maintained.
Many of the needs outlined above are addressed by the present invention hereof. Hence, it is an object of the present invention to provide a mandrel that is durable and effective for bending pipe, as well as easily repaired and maintained.
In accordance with one aspect of the present invention, a mandrel is provided for insertion into a pipe to prevent distortion and buckling while bending the pipe. The mandrel comprises three radial support members distributed along a longitudinal extent of the mandrel. A first radial support member is located at a first end of the mandrel. A second radial support member is located at a second end of the mandrel. A third radial support member is located between the first and second radial support members. A channel is formed in the third radial support member. A leaf spring extends along the longitudinal extent of the mandrel, and the leaf spring is located within the channel. The leaf spring has a first and second spring end. A first end bolt attaches the first spring end to the first radial support member. A second end bolt attaches the second spring end to the second radial support member. The leaf spring is capable of moving relative to the third radial support member within the channel.
In accordance with another aspect of the present invention, a mandrel is provided for insertion into a pipe to prevent distortion and buckling while bending the pipe. The mandrel comprises a compliant member attached to a leaf spring member by a compliant member bolt. The leaf spring member extends along a longitudinal extent of the mandrel. A channel is formed in a radial support member, and the leaf spring member is located within the channel. The channel is shaped and dimensioned such that the compliant member bolt does not contact the channel.
In accordance with yet another aspect of the present invention, a mandrel is provided for insertion into a pipe to prevent distortion and buckling while bending the pipe. The mandrel comprises a plurality of leaf spring members, a plurality of radial support members, and end bolts. Each of the leaf spring members extends along a longitudinal extent of the mandrel. Also, each of the leaf springs has a first spring end and a second spring end. A plurality of compliant members attach to each of the leaf spring members by a corresponding compliant member bolt. The radial support members are distributed along the longitudinal extent of the mandrel. A first radial support member is located at a first end of the mandrel. A second radial support member is located at a second end of the mandrel, and at least one intermediate radial support member is located between the first and second radial support members. A plurality of channels are formed in and distributed along an arcuate direction of each of the radial support members. The leaf spring members are correspondingly located within the channels. Each of the channels is shaped and dimensioned such that none of the compliant member bolts come into contact with any of the channels during use of the mandrel. A first end bolt correspondingly attaches one of the first spring ends to the first radial support member for each of the leaf spring members. A second end bolt correspondingly attaches one of the second spring ends to the second radial support member for each of the leaf spring members. The leaf spring members are capable of moving relative to the at least one intermediate radial support member within the channels formed in the at least one intermediate radial support member.